A prior art device is known from WO 02/063782 A2, which discloses in its FIG. 10 controlled matching stage. This controlled matching stage uses a directional coupler for sampling a forward power signal and a reflected power signal and converts the power signals into control signals. These control signals are supplied to a processing unit, which controls a capacitor bank.
The known device is disadvantageous, inter alia, owing to the fact that it is relatively complex. The power signals need to be converted into control signals. These control signals need to be processed in the processing unit, before it can control the capacitor bank.